The invention relates generally to electric-actuated automotive emission control valves, such as exhaust gas recirculation (EGR) valves, and in particular to improvements that render the actuator more robust.
The actuator of certain EGR valves comprises a solenoid that comprises an electromagnet coil and a stator having an air gap at which magnetic flux acts on an armature. The armature motion is transmitted to a valve element to allow flow through a passageway of the valve. Armature motion is resisted by a return spring that acts on the armature, either directly or via the valve member, to bias the armature to a position that causes the valve element to close the passageway.
The stator air gap is defined by an upper pole piece that is disposed at an upper end of the coil and a lower pole piece at the lower end of the coil. The pole pieces have respective annular hubs that fit into an interior space bounded by the coil, approaching each other from opposite ends of the coil. The juxtaposed ends of the two hubs are spaced apart to define the air gap as an annular space about the armature. Electric current in the coil creates magnetic flux that passes from one hub across the air gap to the armature, through the armature, and back across the air gap to the other hub. The flux causes magnetic force to be applied to the armature, and the axial component of that force acts to displace the armature along the centerline of the solenoid.
The displacement of the valve element is guided by a valve guide bearing that is fit to the valve body. The bearing is cylindrical in shape, comprising a central through-hole through which a stem of the valve element passes with a close sliding fit. The temperature and constituent nature of exhaust gases whose recirculation is controlled by the EGR valve expose the valve and its internal mechanism to harsh operating conditions. When an EGR valve is mounted directly on an engine, it is also subject to engine vibration forces, and those forces may also contribute to harshness that the EGR valve experiences.
It is desirable that such a valve guide bearing comprise a material that can withstand conditions like those described for the full expected life of the EGR valve. An example of such a material is carbon-impregnated bronze.
The solenoid actuator is also exposed to conditions like those described, although possibly to a somewhat lesser extent than are the valve element and its guide bearing. In certain EGR valves, displacement of the solenoid armature must be guided independently of that of the valve element. A known armature guide comprises a non-ferromagnetic guide sleeve that extends between the hubs of the upper and lower pole pieces and within which the armature has a close sliding fit. It is desirable to provide lubricity for minimizing friction between the sleeve and armature, for example by coating the armature and/or guide sleeve with a PTFE-based material. Because of a need for increased control accuracy and increased responsiveness of an EGR valve to control signals applied to its actuator, the interface between such a guide sleeve and armature may become a significant factor in the ability of an EGR valve to achieve the desired degrees of accuracy and responsiveness for the useful life of the valve.
Harsh environmental influences like those described may change the character of the guide sleeve and/or armature as the EGR valve ages, and those changes may have undesired effects on the desired control strategy. For example, certain coatings, such as the polymeric PTFE-based coatings mentioned above may experience deterioration when subjected to extreme heat and vibration, and that deterioration may effect how an EGR valve responds to control signals, thereby affecting a desired control strategy.
Accordingly, improvements in armature guidance that would enable an EGR valve to maintain desired control accuracy and responsiveness over the useful life of the valve are seen to be useful, especially as increasingly strict emission regulations become effective.
It is an object of this invention to provide such improvements in armature guidance in an EGR valve.
One general aspect of the invention relates to an emission control valve for controlling flow of gases with respect to combustion chamber space of an internal combustion engine. The valve comprises a valve body comprising a passageway having an inlet port for receiving gases, an outlet port for delivering gases to the combustion chamber space, a valve element that is selectively positioned to selectively restrict the passage, and a mechanism for selectively positioning the valve element. The mechanism comprises a solenoid having an electromagnet coil, a stator that is associated with the coil and that has a magnetic circuit for conducting magnetic flux generated in the stator when electric current flows in the coil, including an air gap disposed within interior space bounded by the coil, and an armature that is disposed at the air gap and displaced along an imaginary centerline by the magnetic flux to position the valve element. A shaft is pressed into a central axial through-hole in the armature to create a shaft-armature assembly wherein opposite end portions of the shaft protrude from opposite ends of the through-hole. Bearings guide displacement of the shaft-armature assembly along the centerline. An annular lower bearing is fit to a lower pole piece of the stator and an annular upper bearing is fit to an upper pole piece of the stator. The shaft-armature assembly, the upper pole piece, the lower pole piece, and the electromagnet coil are arranged in an assembled relationship to dispose the armature within the interior space bounded by the coil with the end portions of the shaft passing through respective central through-holes in the bearings concentric with the imaginary centerline and with the pole pieces disposed at opposite ends of the coil to create the air gap within the coil interior space and to associate the pole pieces with additional stator structure that conducts magnetic flux between the pole pieces external to the coil interior space.
Another aspect relates to a method of making an emission control valve, as just described, comprising: pressing the shaft into the central axial through-hole in the armature to create a shaft-armature assembly wherein opposite end portions of the shaft protrude from opposite ends of the through-hole; fitting the annular lower bearing to the lower pole piece to create a lower bearing-pole piece assembly; fitting the annular upper bearing to the upper pole piece to create an upper bearing-pole piece assembly; and assembling the shaft-armature assembly, the upper bearing-pole piece assembly, the lower bearing-pole piece assembly, and the electromagnet coil to dispose the armature within the interior space bounded by the coil with the end portions of the shaft passing through the bearing through-holes concentric with the imaginary centerline and with the bearing-pole piece assemblies disposed at opposite ends of the coil to create the air gap within the coil interior space and to associate the pole pieces with additional stator structure that conducts magnetic flux between the pole pieces external to the coil interior space.
The accompanying drawings, which are incorporated herein and constitute part of this specification, include one or more presently preferred embodiments of the invention, and together with a general description given above and a detailed description given below, serve to disclose principles of the invention in accordance with a best mode contemplated for carrying out the invention.